In recent years, from the viewpoint of lower pollution and the like, attention is paid to a hybrid vehicle using an engine and a motor as power sources and traveling while controlling the engine and the motor. In such a hybrid vehicle, a power transmission unit (transaxle) for outputting power obtained from the motor and the engine to a drive shaft via a transmission is mounted. This technique is disclosed in JP2001-164960A, for example.
A hybrid vehicle is requested to have high-precision torque performance for realizing smooth travel. Techniques for testing the hybrid vehicle are disclosed in, for example, JP2004-219354A and JP2005-140668A. Specifically, JP2004-219354A discloses a technique for testing the performance of a motor and capable of specifying the cause of a failure.
JP2005-140668A discloses a technique for testing the performance of a transaxle including two motors and a differential device and capable of specifying the cause of a failure.
However, the aforementioned conventional hybrid vehicle testing techniques have the following problems. Specifically, the testing techniques disclosed in JP2004-219354A and JP2005-140668A relate to tests for a single motor or a single transaxle but not tests to be conducted in a state where the motor or transaxle is combined with an inverter. On the other hand, when the motor is tested in a vehicle state as a final product form, abnormal output characteristics of the motor are detected not only when the motor is defective but also when the inverter is defective. In such cases, according to the conventional testing techniques, it is impossible to distinguish whether the failure is caused by abnormality of the motor itself, breakdown of the inverter that drives the motor, or a combination thereof. Consequently, in the case where a failure is detected in the vehicle state (for example, a failure which occurs in a general test just before shipment or in use), the region of the failure, which is in the motor itself or in a part combined with the inverter, cannot be specified, so that the whole hybrid system has to be replaced.